The present invention relates to an apparatus for automatically adjusting the gap between a platen and a printing head in proportion to the corresponding thickness of recording paper.
With recording heads, particularly wire dot recording heads for use in printing characters by striking wires against recording paper via ink ribbons, the striking strokes of the wire have to be set as small as possible in order to effect high-speed printing.
On the other hand, since the wire dot recording head must be strong in mechanical strength, to render it possible to make copies with the aid of a copying material, such printers are very versatile in the kinds of recording paper which they are capable of utilizing. Consequently, unlike other types of printers, for this kind of printer, the distance between the recording head and recording paper tends to vary to a greater extent.
For this reason, printers using wire dot recording heads are usually provided with a mechanism for adjusting the relative gap between the platen and the recording head. However, the problem is that selecting the optimum gap for a specific type of recording paper requires a great deal of skill and is also troublesome.
In order to solve the problem above, Examined Japanese Patent Publication No. Hei. 4-14634, for instance, discloses a printer providing an encoder for producing pulse signals corresponding to the movement of a carriage from the initial position and a control unit for processing feedback pulse signals from the encoder. In this case, when a recording head abuts against recording paper, the fact that a pulse motor for driving the carriage starts stepping out is detected from variations in the number of pulses from the encoder. The thickness of the recording paper is obtained from the movement of the carriage up to the point in time of abutment, so that the carriage position is made controllable according to the data thus obtained.
Notwithstanding, there still arises a problem in that, since the recording head is forced to abut against the recording paper until the pulse motor starts to step out, recording paper such as copying paper which colors in response to external force may bear press marks.